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Group 1: the alkali metals
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Lithium, sodium and potassium are soft metals that react quickly with water. They get more reactive down the group.
Properties
Soft (can be cut with a knife), low density, low melting points.
Stored under oil to stop them reacting with air and water.
Stored under oil to stop them reacting with air and water.
Reaction with water
metal + water → metal hydroxide + hydrogen
2Na + 2H2O → 2NaOH + H2
The hydroxide makes the solution alkaline.
Lithium fizzes; sodium melts into a ball and whizzes around; potassium burns with a lilac flame.
2Na + 2H2O → 2NaOH + H2
The hydroxide makes the solution alkaline.
Lithium fizzes; sodium melts into a ball and whizzes around; potassium burns with a lilac flame.
Why reactivity increases down the group
All have one outer electron, which they lose to form a 1+ ion.
Down the group, atoms are bigger, so the outer electron is further from the nucleus and more shielded. It is lost more easily.
Down the group, atoms are bigger, so the outer electron is further from the nucleus and more shielded. It is lost more easily.
Predict how rubidium reacts with water.
- Rubidium is below potassium.
- So it is even more reactive: very violent, possibly explosive.
Answer: Even more violently than potassium.
Group 1 metals are soft and stored under oil. With water they form an alkaline hydroxide and hydrogen. Reactivity increases down the group because the outer electron is lost more easily.
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